Rare Earth Metals from Fly Ash

July 7, 2016

In graduate school, I once saw a version of the periodic table called "The Boron Chemist's Periodic Table." My first thought was why would anyone care so much about a single element to call himself a "boronchemist." Could such a single-minded chemist be instead called a "boring chemist?" That aside, the table I saw was distorted to show the boron box many times larger than those of the other elements.

"The Department of Energy is investing $20 million into research on extraction technologies for coal wastes, and there is literally billions of dollars' worth of rare earth elements contained in our nation's coal ash... If a program were to move forward, they'd clearly want to pick the coal ash with the highest amount of extractable rare earth elements, and our work is the first comprehensive study to begin surveying the options."[7]

Nitric acid could possibly be used in a commercial extraction process, so extraction was tried using this acid. Appalachian Mountain coal ash is typically encapsulated in a glassy matrix of aluminum silicates, which makes it relatively insoluble in nitric acid, while the Powder River Basin ash dissolved better.[7] The fraction of "critical" rare earth elements (Nd, Eu, Tb, Dy, Y, and Er) in the fly ashes was 34-38% of the total rare earth concentration, which is quite a bit higher than that in conventional ores (usually less than 15%).[6]